For example, in a liquid crystal display, a light guiding plate for guiding the light of a back light over a whole display screen is provided on the back side of the display surface of a liquid crystal panel. In the light guiding plate of this kind, an incident light is introduced from the end face side of the light guiding plate or an optical waveguide and is totally reflected and propagated in the light guiding plate or the optical waveguide so that a planar total reflected light can be obtained efficiently.
Moreover, a reflector capable of carrying out an efficient reflection includes a film having a metal or a metallic surface. In addition, the reflector includes a multilayer film interference mirror such as a dielectric multilayer film mirror.
FIG. 31 shows a state in which an incident light is introduced from a general light guiding plate and waveguide according to the conventional art. FIG. 31(a) shows a state in which the incident light is introduced from the end face of the light guiding plate and is totally reflected and guided in the light guiding plate, and FIG. 31(b) shows a state in which a prism is provided on the end of the light guiding plate and the incident light is introduced through the prism and is totally reflected and guided in the light guiding plate. Moreover, FIG. 31(c) shows a state in which the incident light is introduced from the end of the waveguide formed on a substrate into the waveguide and is totally reflected and guided in the waveguide.
The light guiding plate and the waveguide satisfy total reflecting conditions in the light guiding plate and the waveguide by introducing the incident light at a greater angle than a total reflecting critical angle. Moreover, the light guiding plate and the waveguide have been expected to be developed into various optical devices or optical systems which utilize a total reflection in the future.
As described above, in the conventional method of introducing the incident light into the light guiding plate and the waveguide, the incident light is introduced from the end face side of the light guiding plate and the waveguide or is introduced through the prism connected to the end on either surface side of the light guiding plate. In the light guiding plate and the waveguide which are thin and plate-shaped, however, the incidence opening area of the end face is small and a coupling efficiency with the incident light tends to be deteriorated. Moreover, the light guiding plate and the waveguide have been desired to have a smaller thickness and a larger area, and the incidence opening area of the end face tends to be reduced increasingly. Consequently, there is a fear that the coupling efficiency might be deteriorated. Furthermore, the shape of the incident light (a light source) and an introducing position are restricted and the size and number of the light sources is limited so that a light having a high output cannot be introduced. Moreover, the incident light is to be beam-shaped or linear so that the type of the light source is restricted and an optical system for acquiring the shape described above is required.
In the case in which the reflector is a film having a metal or a metallic surface, moreover, an absorption is carried out at time of a reflection so that a light loss is always caused. In the case of the multilayer film interference mirror, a transmitted light is present when the incidence angle of the incident light is increased. For this reason, it is impossible to obtain a perfect reflector having a high efficiency for an optional incidence angle.